In order to realize color printing, the image forming apparatus superimposes images formed by toners of different colors. Here, a color shift in which the superimposition of the different images is not ideal may result when the different toner images are shifted in position from each other because of misalignments of the different imaging units for each. The cause of color shift may be a displacement in each color unit due to the temperature variation of optical scanning devices or the like. For this reason, the image forming apparatus generally corrects colors shift by executing an alignment process when the temperature of an optical scanning device changes by a certain level or more. However, it is desired to further suppress color shifts occurring in image forming apparatuses.